1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to improvements of dimples of golf balls.
2. Description of the Related Art
Golf balls have numerous dimples on the surface thereof. In general, golf balls have single radius dimples having a cross-sectional shape with single curvature radius, or double radius dimples having a cross-sectional shape with two curvature radii. The dimples disrupt the air flow around the golf ball during flight to cause turbulent flow separation. By causing the turbulent flow separation, separating points of the air from the golf ball shift backwards leading to the reduction of a drag. The turbulent flow separation promotes the differentia between the separating point on the upper side and the separating point on the lower side of the golf ball, which result from the backspin, thereby enhancing the lift force that acts upon the golf ball. Such a role of the dimples is referred to as a “dimple effect”. Excellent dimples disturb the air flow more efficiently.
A variety of proposals with respect to the sectional shape of the dimples in attempts to improve flight performances have been made. U.S. Pat. No. 5,338,039 discloses dimples having a shape with the gradient of a slope disposed in the vicinity of the edge being greater than that of a slope at the bottom part. U.S. Pat. No. 5,735,757 discloses dimples having a cross-sectional shape given by double radius.
When a golf ball is hit with a short iron, the surface thereof may be scuffed. In case of golf balls having double radius dimples, in particular, margin of the dimple is liable to be scuffed resulting from concentration of the stress. There also remains room for improvement of the double radius dimple in respect of the scuff resistance. An object of the present invention is to provide a golf ball that is excellent in the flight performance and scuff resistance.